1. Field of Invention
The present invention relates to a method for making a gas sensor and, more particularly, to a method for making a nano-composite gas sensor.
2. Related Prior Art
Disclosed in U.S. Pat. No. 6,759,010 is an sensor array. The resistances of the sensors are used to form a fingerprint-like pattern for sensing gases. The sensing of the gases is important in the industry such as the semiconductor industry in which ammonia is used together with many other gases. The sensor array includes more than two polymers on an electrode before the electrode is connected to other electrodes. The sensor array provides a warning when it contacts hazardous gas.
As disclosed in U.S. Pat. No. 6,929,735, an ion-type polymer film is coated on electrodes of a sensor. The sensitivity of the gas sensor is good because gas directly reaches the electrodes.
As disclosed in U.S. Pat. No. 5,674,752, a gas-sensing module includes a single resistance-type sensor or multiple resistance-type sensors connected to one another. One or more conductive polymers are coated on the electrodes of the gas-sensing module. The resistances of the sensors change as the polymer coated on the electrodes expands to different extents as it absorbs the gas. Thus, a fingerprint-like pattern is formed for the sensing of the gas. This gas-sensing module can be used to detect DMMP.
Disclosed in U.S. Pat. No. 7,186,799 is an array of surface acoustic wave (“SAW”) sensors. Changes in the frequencies of the SAW sensors are used to form a fingerprint-like pattern for sensing gases. The spirit is to increase the sensitivity by increasing the oscillation frequencies of the SAW sensors or coating the SAW sensors with an organic material. Thus, the frequencies of the SAW sensors change as the SAW sensors contact hazardous gas, and the SAW gas-sensing module provides a warning.
The use of the above-mentioned patents is not without problems. At first, in a composite manner, multiple peptides or a multi-component peptide is mixed with a nano-conductive material such as carbon black so that the conductive material is evenly suspended in the peptide-based mixture. Thus, a composite film is made. It is not without any problems to disperse the various peptides or the multi-component peptide in the solvent, the sorts of the peptides or the components of the peptide are limited.
Secondly, carbon black, a kind of zero-dimension material, is used as the nano-conductive material. Carbon black, which exhibits inadequate mechanical properties and deformability, cannot be recovered adequately. Therefore, the sensitivity and repeatability are inadequate.
Thirdly, to make the conventional arrays of sensors, various polymers are mixed with nano-conductive materials. The making of the sensors is not easy because of the compatibility of the polymer and nano-conductive material with the solvent.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.